Organic light-emitting diode, organic light-emitting display including the same, and method of manufacturing the same

ABSTRACT

An organic light-emitting diode includes: a first electrode, a light-emitting stack thereon including, sequentially stacked: a hole transport layer (HTL) including an HTL material, a blue light-emitting layer including: a blue host material (BHM) and a blue fluorescent dopant (BFD) material, and an electron transport layer (ETL) including an ETL material, and a second electrode on the light-emitting stack, wherein the BFD material has a higher LUMO, a higher HOMO, and a lower singlet energy than the BHM, the HTL material has a higher HOMO than the BHM and the BFD material, a difference in HOMO between the HTL material and the BFD material is 0.1 eV or less, the ETL material has a higher LUMO than the BHM and the BFD material, and a difference in LUMO between the ETL material and the BFD material is 0.1 eV or less.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of and priority to Korean PatentApplication No. 10-2017-0178314, filed on Dec. 22, 2017, the entirety ofwhich is hereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to an organic light-emitting diode, anorganic light-emitting display including the same, and a method ofmanufacturing the same.

2. Discussion of the Related Art

Recently, there is increasing interest in flat-panel display elementsoccupying a small space, with increasing size of displays. A technologyof an organic light-emitting display including organic light-emittingdiodes (OLEDs) as the flat-panel display elements has been rapidlydeveloped in the art.

An organic light-emitting diode emits light through conversion of energyof excitons created by pairs of electrons and holes generated uponinjection of charges into an organic light-emitting layer formed betweenan anode and a cathode. As compared with exiting display techniques, theorganic light-emitting diode has various advantages, such as low voltageoperation, low power consumption, good color reproduction, and variousapplications through application of a flexible substrate.

Generally, OLEDs can be classified into a single OLED and a tandem OLED.The tandem OLED is an OLED including two or more light-emitting stacksand allows easier improvement in operation voltage and efficiency thanan existing single OLED.

In a typical white organic light-emitting diode (WOLED), a difference inenergy level between functional layers constituting a bluelight-emitting layer deteriorates efficiency in injection of electronsor holes at an interface between the functional layers, thereby having anegative influence on performance and lifespan of the WOLED.

SUMMARY

Accordingly, embodiments of the present disclosure are directed to anorganic light-emitting diode, an organic light-emitting displayincluding the same, and a method of manufacturing the same thatsubstantially obviate one or more of the issues due to limitations anddisadvantages of the related art.

An aspect of the present disclosure is to provide an organiclight-emitting diode capable of reducing operation voltage whileimproving luminous efficacy and lifespan thereof, and an organiclight-emitting display including the same.

An aspect of the present disclosure is to provide an organiclight-emitting diode that may include a blue light-emitting layer whilesecuring improved operation characteristics and long lifespan.

Additional features and aspects will be set forth in the descriptionthat follows, and in part will be apparent from the description, or maybe learned by practice of the inventive concepts provided herein. Otherfeatures and aspects of the inventive concepts may be realized andattained by the structure particularly pointed out in the writtendescription, or derivable therefrom, and the claims hereof as well asthe appended drawings.

To achieve these and other aspects of the inventive concepts as embodiedand broadly described, there is provided an organic light-emittingdiode, including: a first electrode, a light-emitting stack on the firstelectrode including, sequentially stacked on the first electrode: a holetransport layer including a hole transport layer material, a bluelight-emitting layer including: a blue host material, and a bluefluorescent dopant material, and an electron transport layer includingan electron transport layer material, and a second electrode on thelight-emitting stack, wherein the blue fluorescent dopant material has ahigher LUMO (Lowest Unoccupied Molecular Orbital) energy level than theblue host material, wherein the blue fluorescent dopant material has ahigher HOMO (Highest Occupied Molecular Orbital) energy level than theblue host material, wherein the blue fluorescent dopant material has alower singlet energy than the blue host material, wherein the holetransport layer material has a higher HOMO energy level than the bluehost material, wherein the hole transport layer material has a higherHOMO energy level than the blue fluorescent dopant material, wherein adifference in HOMO energy level between the hole transport layermaterial and the blue fluorescent dopant material is 0.1 eV or less,wherein the electron transport layer material has a higher LUMO energylevel than the blue host material, and wherein the electron transportlayer material has a higher LUMO energy level than the blue fluorescentdopant material, and wherein a difference in LUMO energy level betweenthe electron transport layer material and the blue fluorescent dopantmaterial is 0.1 eV or less.

In another aspect, there is provided a method of manufacturing anorganic light-emitting diode, the method including: providing a firstelectrode, providing a light-emitting stack on the first electrodeincluding, sequentially stacking on the first electrode: a holetransport layer including a hole transport layer material, a bluelight-emitting layer including: a blue host material, and a bluefluorescent dopant material, and an electron transport layer includingan electron transport layer material, and providing a second electrodeon the light-emitting stack, wherein the blue fluorescent dopantmaterial has a higher LUMO (Lowest Unoccupied Molecular Orbital) energylevel than the blue host material, wherein the blue fluorescent dopantmaterial has a higher HOMO (Highest Occupied Molecular Orbital) energylevel than the blue host material, wherein the blue fluorescent dopantmaterial has a lower singlet energy than the blue host material, whereinthe hole transport layer material has a higher HOMO energy level thanthe blue host material, wherein the hole transport layer material has ahigher HOMO energy level than the blue fluorescent dopant material,wherein a difference in HOMO energy level between the hole transportlayer material and the blue fluorescent dopant material is 0.1 eV orless, wherein the electron transport layer material has a higher LUMOenergy level than the blue host material, wherein the electron transportlayer material has a higher LUMO energy level than the blue fluorescentdopant material, and wherein a difference in LUMO energy level betweenthe electron transport layer material and the blue fluorescent dopantmaterial is 0.1 eV or less.

Other systems, methods, features and advantages will be, or will become,apparent to one with skill in the art upon examination of the followingdrawings and detailed description. It is intended that all suchadditional systems, methods, features and advantages be included withinthis description, be within the scope of the present disclosure, and beprotected by the following claims. Nothing in this section should betaken as a limitation on those claims. Further aspects and advantagesare discussed below in conjunction with embodiments of the disclosure.It is to be understood that both the foregoing general description andthe following detailed description of the present disclosure areexamples and explanatory, and are intended to provide furtherexplanation of the disclosure as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, that may be included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this specification, illustrate embodiments of the disclosure andtogether with the description serve to explain various principles of thedisclosure.

FIG. 1 is an energy diagram depicting energy levels of a hole transportlayer (HTL), a blue light-emitting layer (B-EML), and an electrontransport layer (ETL) of an organic light-emitting diode according to anembodiment of the present disclosure.

FIG. 2 is a sectional view of an organic light-emitting diode accordingto one example embodiment of the present disclosure.

FIG. 3 is a sectional view of an organic light-emitting diode accordingto another example embodiment of the present disclosure.

FIG. 4 is a sectional view of an organic light-emitting diode accordingto a further example embodiment of the present disclosure.

FIG. 5 is a sectional view of an organic light-emitting displayaccording to one example embodiment of the present disclosure.

FIG. 6 is an energy diagram depicting energy levels of an organiclight-emitting diode of Example 1.

FIG. 7 is an energy diagram depicting energy levels of an organiclight-emitting diode of Comparative Example 1.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals should be understood torefer to the same elements, features, and structures. The relative sizeand depiction of these elements may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the presentdisclosure, examples of which may be illustrated in the accompanyingdrawings. In the following description, when a detailed description ofwell-known functions or configurations related to this document isdetermined to unnecessarily cloud a gist of the inventive concept, thedetailed description thereof may be omitted. The progression ofprocessing steps and/or operations described is an example; however, thesequence of steps and/or operations is not limited to that set forthherein and may be changed as is known in the art, with the exception ofsteps and/or operations necessarily occurring in a particular order.Like reference numerals designate like elements throughout. Names of therespective elements used in the following explanations are selected onlyfor convenience of writing the specification and may be thus differentfrom those used in actual products.

Advantages and features of the present disclosure, and implementationmethods thereof will be clarified through following example embodimentsdescribed with reference to the accompanying drawings. The presentdisclosure may, however, be embodied in different forms and should notbe construed as limited to the example embodiments set forth herein.Rather, these example embodiments are provided so that this disclosuremay be sufficiently thorough and complete to assist those skilled in theart to fully understand the scope of the present disclosure. Further,the present disclosure is only defined by scopes of claims.

A shape, a size, a ratio, an angle, and a number disclosed in thedrawings for describing embodiments of the present disclosure are merelyan example. Thus, the present disclosure is not limited to theillustrated details. Like reference numerals refer to like elementsthroughout. In the following description, when the detailed descriptionof the relevant known function or configuration is determined tounnecessarily obscure an important point of the present disclosure, thedetailed description of such known function or configuration may beomitted. In a case where terms “comprise,” “have,” and “include”described in the present specification are used, another part may beadded unless a more limiting term, such as “only,” is used. The terms ofa singular form may include plural forms unless referred to thecontrary.

In construing an element, the element is construed as including an erroror tolerance range even where no explicit description of such an erroror tolerance range. In describing a position relationship, when aposition relation between two parts is described as, for example, “on,”“over,” “under,” or “next,” one or more other parts may be disposedbetween the two parts unless a more limiting term, such as “just” or“direct(ly),” is used.

In describing a time relationship, when the temporal order is describedas, for example, “after,” “subsequent,” “next,” or “before,” a casewhich is not continuous may be included unless a more limiting term,such as “just,” “immediate(ly),” or “direct(ly),” is used.

It will be understood that, although the terms “first,” “second,” etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure.

In describing elements of the present disclosure, the terms like“first,” “second,” “A,” “B,” “(a),” and “(b)” may be used. These termsare merely for differentiating one element from another element, and theessence, sequence, order, or number of a corresponding element shouldnot be limited by the terms. Also, when an element or layer is describedas being “connected,” “coupled,” or “adhered” to another element orlayer, the element or layer can not only be directly connected oradhered to that other element or layer, but also be indirectly connectedor adhered to the other element or layer with one or more interveningelements or layers “disposed” between the elements or layers, unlessotherwise specified.

The term “at least one” should be understood as including any and allcombinations of one or more of the associated listed items. For example,the meaning of “at least one of a first item, a second item, and a thirditem” denotes the combination of all items proposed from two or more ofthe first item, the second item, and the third item as well as the firstitem, the second item, or the third item.

In the description of embodiments, when a structure is described asbeing positioned “on or above” or “under or below” another structure,this description should be construed as including a case in which thestructures contact each other as well as a case in which a thirdstructure is disposed therebetween. The size and thickness of eachelement shown in the drawings are given merely for the convenience ofdescription, and embodiments of the present disclosure are not limitedthereto.

Features of various embodiments of the present disclosure may bepartially or overall coupled to or combined with each other, and may bevariously inter-operated with each other and driven technically as thoseskilled in the art can sufficiently understand. Embodiments of thepresent disclosure may be carried out independently from each other, ormay be carried out together in co-dependent relationship.

In accordance with one aspect of the present disclosure, there may beprovided an organic light-emitting diode including: a first electrode, alight-emitting stack on the first electrode, and a second electrode onthe light-emitting stack. The light-emitting stack may include a holetransport layer, a blue light-emitting layer, and an electron transportlayer. The hole transport layer, the blue light-emitting layer, and theelectron transport layer may be sequentially stacked on the firstelectrode.

The blue light-emitting layer may include a blue host material and ablue fluorescent dopant material. The hole transport layer may include ahole transport layer material. The electron transport layer may includean electron transport layer material.

The light-emitting stack may satisfy the following energy levelconditions (A) to (G):

(A) The blue fluorescent dopant material has a higher LUMO energy levelthan the blue host material;

(B) the blue fluorescent dopant material has a higher HOMO energy levelthan the blue host material;

(C) the blue fluorescent dopant material has a lower singlet energy thanthe blue host material;

(D) the hole transport layer material has a higher HOMO energy levelthan the blue host material;

(E) the hole transport layer material has a higher HOMO energy levelthan the blue fluorescent dopant material and a difference in HOMOenergy level between the hole transport layer material and the bluefluorescent dopant material is 0.1 eV or less;

(F) the electron transport layer material has a higher LUMO energy levelthan the blue host material; and

(G) the electron transport layer material has a higher LUMO energy levelthan the blue fluorescent dopant material and a difference in LUMOenergy level between the electron transport layer material and the bluefluorescent dopant material is 0.1 eV or less.

The organic light-emitting diode, including the light-emitting stacksatisfying the energy level conditions of the blue fluorescent dopantmaterial and the blue host material, may facilitate injection andrecombination of electrons and holes in the blue light-emitting layer.Excitons can be generated only within the light-emitting layer, therebyimproving operation characteristics and lifespan thereof.

Further, in the organic light-emitting diode, including the holetransport layer satisfying the HOMO energy level condition of the holetransport layer material, holes may be injected into the light-emittinglayer through the hole transport layer at an anode, and the bluefluorescent dopant material forming the light-emitting layer may exhibitstrong hole characteristics. In this case, a small difference in HOMOenergy level may be set between the blue fluorescent dopant materialexhibiting the hole characteristics and the hole transport layer,thereby improving hole injection from the hole transport layer into thelight-emitting layer. With this structure, the organic light-emittingdiode can achieve improvement in operation characteristics and longlifespan.

In the organic light-emitting diode, which may include thelight-emitting stack including the blue light-emitting layer and thehole transport layer satisfying the LUMO energy level conditions of theblue host material, the blue fluorescent dopant material, and the holetransport layer material, distribution of electrons may be restricted inthe blue light-emitting layer, thereby enabling efficient control ofgeneration of excitons. In addition, the organic light-emitting diodemay prevent excitons generated in the blue light-emitting layer frommigrating into the hole transport layer, thereby preventing additionreaction and energy loss due to the excitons. As a result, the organiclight-emitting diode may prevent variation in charge migrationcharacteristics due to impurities generated by addition reaction, whichcan be generated by excitons having migrated to the hole transportlayer, and may maintain operation characteristics thereof. Further, inthe organic light-emitting diode, a site where exciton energy is usedmay be restricted in the blue light-emitting layer, thereby improvingluminous efficacy. With this structure, the organic light-emitting diodecan achieve improvement in operation characteristics and long lifespan.

In the organic light-emitting diode, in which the blue host material,the blue fluorescent dopant material and the electron transport layersatisfying the LUMO energy level conditions may be interposed betweenthe second electrode and the blue light-emitting layer, electronstransported from the second electrode may be effectively injected intothe blue light-emitting layer, thereby enabling efficient control ofgeneration of excitons. With this structure, the organic light-emittingdiode can achieve improvement in operation characteristics and longlifespan.

FIG. 1 is an energy diagram depicting energy levels of a hole transportlayer (HTL), a blue light-emitting layer (B-EML) and an electrontransport layer (ETL) of an organic light-emitting diode according to anexample embodiment of the present disclosure.

In FIG. 1, the blue light-emitting layer (B-EML) may include a bluefluorescent dopant material (BD) and a blue host material (BH). Withreference to the example of FIG. 1, the energy level of each layer inthe organic light-emitting diode satisfies Conditions (A) to (G). Forexample, as shown in FIG. 1, (A) the blue fluorescent dopant material(BD) has a higher LUMO energy level than the blue host material (BH). Inaddition, as shown in FIG. 1, (B) the blue fluorescent dopant material(BD) has a higher HOMO energy level than the blue host material (BH). InFIG. 1, (C) the blue fluorescent dopant material (BD) has a lowersinglet energy than the blue host material (BH). In FIG. 1, (D) the holetransport layer (HTL) material has a higher HOMO energy level than theblue host material (BH). In FIG. 1, ΔE₁ is caused by Condition (E)wherein the hole transport layer (HTL) material has a higher HOMO energylevel than the blue fluorescent dopant material (BD). A difference inHOMO energy level between the hole transport layer material and the bluefluorescent dopant material is 0.1 eV or less. For example, ΔE₁≤0.1 eV.In FIG. 1, (F) the electron transport layer (ETL) material has a higherLUMO energy level than the blue host material (BH). In FIG. 1, ΔE₂ iscaused by Condition (G) wherein the electron transport layer (ETL)material has a higher LUMO energy level than the blue fluorescent dopantmaterial (BD). A difference in LUMO energy level between the electrontransport layer (ETL) material and the blue fluorescent dopant material(BD) is 0.1 eV or less. For example, ΔE₂≤0.1 eV.

FIG. 2 is a sectional view of an organic light-emitting diode accordingto one example embodiment of the present disclosure.

FIG. 2 is a sectional view of an organic light-emitting diode 100according to one example embodiment of the present disclosure, which mayinclude a first electrode 110, a light-emitting stack 140, and a secondelectrode 120. The light-emitting stack 140 may include a hole transportlayer (HTL) 141, a blue light-emitting layer (B-EML) 142 adjoining thehole transport layer (HTL) 141, and an electron transport layer (ETL)144 adjoining the blue light-emitting layer (B-EML) 142.

The first electrode 110 may be an anode through which holes may beinjected into the organic light-emitting diode, and may be formed of aconductive material having a high work function. For example, the firstelectrode 110 may include one or more of: indium tin oxide (ITO), indiumzinc oxide (IZO), and/or zinc oxide (ZnO). Embodiments are not limitedto these examples.

The second electrode 120 may be a cathode through which electrons may beinjected into the organic light-emitting diode, and may be formed of aconductive material having a low work function. For example, the secondelectrode 120 may include one or more of: aluminum (Al), magnesium (Mg),and/or an aluminum-magnesium alloy (AlMg). Embodiments are not limitedto these examples.

The light-emitting stack 140 may include the hole transport layer (HTL)141, the blue light-emitting layer (BML) 142, and the electron transportlayer (ETL) 144 interposed between the first electrode 110 and thesecond electrode 120. The hole transport layer (HTL) 141 may beinterposed between the first electrode 110 and the blue light-emittinglayer (B-EML) 142.

The hole transport layer (HTL) 141 may include one or more of:N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD),NPD, MTDATA, 1,3-bis(N-carbazolyl)benzene (mCP), CuPC, TCTA,tris(trifluorovinylether)-tris(4-carbazolyl-9-yl-phenyl)amine(TFV-TCTA), tris[4-(diethylamino)phenyl]amine,N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluorene-2-amine,tri-p-tolylamine,N-[1,1′-biphenyl]-4-yl-9,9-dimethyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine,4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP),1,1-bis(4-(N,N′-di(p-tolyl)amino)phenyl)cyclohexane (TAPC), and/orcombinations thereof. Embodiments are not limited to these examples.

In one embodiment, the hole transport layer (HTL) material may be atertiary amine compound. The blue light-emitting layer (B-EML) 142 mayinclude a blue host material (BH) and a blue fluorescent dopant material(BD). In one embodiment, the blue host material (BH) may include ananthracene-based material. For example, the blue host material (BH) mayinclude one or more of: 9,10-di-(2-naphtyl)anthracene (ADN),2-tert-butyl-9,10-di(2-naphthyl)anthracene,2-methyl-9,10-di(2-naphtyl)anthracene (MADN), and/or combinationsthereof. Embodiments are not limited to these examples.

In one embodiment, the blue fluorescent dopant material (BD) may includea pyrene amine derivative material. For example, the blue fluorescentdopant material (BD) may include one or more of:1,6-bis(diphenylamine)pyrene, TBPe(tetrakis(t-butyl)perylene), and/orcombinations thereof, without being limited thereto.

The blue light-emitting layer (B-EML) 142 may include 1% by weight (wt%) to 5 wt % of the blue fluorescent dopant material (BD). Within thiscontent of the blue fluorescent dopant material (BD), the bluelight-emitting layer (B-EML) 142 can effectively satisfy the energylevel conditions described above. If the content of the blue fluorescentdopant material (BD) exceeds this range, concentration extinction canoccur between dopant materials, thereby causing deterioration inefficiency at high brightness. If the content of the blue fluorescentdopant material (BD) is less than this range, energy transfer from ahost to a dopant becomes difficult, thereby making it difficult toobtain a desired level of luminous characteristics while causingreduction in lifespan of the organic light-emitting diode due to sidereaction in the light-emitting layer.

The electron transport layer (HTL) may be between the bluelight-emitting layer (B-EML) 142 and the second electrode 120 and servesto secure efficient transport of electrons. For example, the electrontransport layer (HTL) material may include derivatives, such asoxadiazole, triazole, phenanthroline, benzoxazole, benzothiazole,benzimidazole, triazine, and the like. Embodiments are not limited tothese examples.

For example, the electron transport layer (HTL) 144 may include anelectron transport material including one or more of: Alq3,2-biphenyl-4-yl-5-(4-tbutylphenyl)-1,3,4-oxadiazole (PBD), spiro-PBD,lithium quinolate (Liq),2-[4-(9,10-Di-2-naphthalenyl-2-anthracenyl)phenyl]-1-phenyl-1H-benzimidazol,3-(biphenyl-4-yl)-5-(4-tertbutyl phenyl)-4-phenyl-4H-1,2,4-triazole(TAZ), 4,7-diphenyl-1,10-phenanthroline (Bphen), tris(phenylquinoxaline)(TPQ), 1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene (TmPyPB),1,3,5-tris(N-phenylbenzimiazole-2-yl)benzene (TPBI), and/or combinationsthereof. Embodiments are not limited to these examples. For example, theelectron transport layer (HTL) material may be a pyrimidine-basedmaterial.

Optionally, the electron transport layer (HTL) 144 may be formed bydoping with an alkali metal or alkali earth metal compound. Examples ofmetal components that can be used as a dopant for the electron transportlayer (HTL) 144 may include alkali metals, such as lithium (Li), sodium(Na), potassium (K) and cesium (Cs); and alkali earth metals, such asmagnesium (Mg), strontium (Sr), barium (Ba), and radium (Ra), withoutbeing limited thereto. The alkali metal or alkali earth metal compoundmay be present in an amount of about 1 wt % to 20 wt %, without beinglimited thereto.

The light-emitting stack 140 may optionally further include a holeinjection layer (HIL) and an electron transport layer (ETL), as desired.The hole injection layer (HIL) may be between the first electrode 120and the hole transport layer (HTL) 142. The hole injection layer (HIL)may improve interface characteristics between the first electrode 120formed of an inorganic material and the hole transport layer (HTL) 142formed of an inorganic material.

For example, the hole injection layer (HIL) may include one or more of:4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (MTDATA), copperphthalocyanine (CuPc), tris(4-carbazolyl-9-yl-phenyl)amine (TCTA),N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4″-diamine (NPB,NPD), 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HATCN),1,3,5-tris[4-(diphenylamino)phenyl]benzene (TDAPB),poly(3,4-ethylenedioxythiphene)polystyrene sulfonate (PEDOT/PSS),2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ),N-(biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)-9H-fluoren-2-amine,and combinations thereof. Embodiments are not limited to these examples.

The electron injection layer (EIL) may be between the electron transportlayer (ETL) and the second electrode 120 and serves to secure efficientinjection of electrons. For example, the electron injection layer (EIL)may include at least one selected from the group consisting of alkalihalides, such as LiF, NaF, KF, RbF, CsF, FrF, BeF₂, MgF₂, CaF₂, SrF₂,BaF₂ and RaF₂, organic materials, such as Liq (lithium quinolate),lithium benzoate, sodium stearate, Alq₃, BAlq, PBD, spiro-PBD, and TAZ,and combinations thereof.

FIG. 3 is a sectional view of an organic light-emitting diode accordingto another example embodiment of the present disclosure.

In FIG. 3, an organic light-emitting diode 200 according to anotherexample embodiment of the present disclosure may include a firstelectrode 210, a light-emitting stack 240 and a second electrode 220.With reference to FIG. 3, the light-emitting stack 240 may include ahole injection layer (HIL) 243, a hole transport layer (HTL) 241, a bluelight-emitting layer (B-EML) 242, an electron transport layer (ETL) 244,and an electron injection layer (EIL) 245. Details of the layers stackedin the organic light-emitting diode 200 according to this embodiment aresubstantially similar to those of the above embodiment, and detaileddescription thereof will be omitted.

The organic light-emitting diode may have a tandem structure includingat least two light-emitting stacks. In one embodiment, each of thelight-emitting stacks 142, 242 may be a first light-emitting stack, andthe organic light-emitting diode may further include at least oneadditional light-emitting stack including a second light-emitting stackbetween the first electrode and the second electrode.

FIG. 4 is a sectional view of an organic light-emitting diode accordingto a further example embodiment of the present disclosure.

In FIG. 4, an organic light-emitting diode 300 according to a furtherexample embodiment of the present disclosure may include a firstelectrode 310, a first light-emitting stack (ST1) 340, a chargegeneration layer (CGL) 360, a second light-emitting stack (ST2) 350, anda second electrode 320. With reference to FIG. 4, the firstlight-emitting stack (ST1) 340 may include a first hole transport layer(HTL) 341, a first blue light-emitting layer 342, and a first electrontransport layer (ETL) 344. The second light-emitting stack (ST2) 350 mayinclude a second hole transport layer (HTL) 351, a second bluelight-emitting layer 352, and a second electron transport layer (ETL)354. In addition, each of the first light-emitting stack (ST1) 340 andthe second light-emitting stack (ST2) 350 may further include an organiclayer, such as a hole injection layer, a hole transport layer, anelectron transport layer, and an electron injection layer, as desired.Details of the layers stacked in the organic light-emitting diode 300according to this embodiment are substantially similar to those of theabove embodiment, and detailed description thereof will be omitted.

In the organic light-emitting diode 300, the charge generation layer(CGL) 360 may be between the first light-emitting stack (ST1) 340 andthe second light-emitting stack (ST2) 350, e.g., to improve currentefficiency in each of the light-emitting layers while securing efficientdistribution of charges. For example, the charge generation layer 360may be between first light-emitting stack (ST1) 340 and the secondlight-emitting stack (ST2) 350. The first light-emitting stack (ST1) 340may be connected to the second light-emitting stack (ST2) 350 by thecharge generation layer 360. The charge generation layer 360 may be a PNjunction charge generation layer in which an N-type charge generationlayer 362 may adjoin a P-type charge generation layer 364.

The N-type charge generation layer 362 may face the first light-emittingstack (ST1) 340, and the P-type charge generation layer 364 may face thesecond light-emitting stack (ST2) 350. The charge generation layer 360may generate charges or may divide the charges into holes and electronsto supply the holes and electrons to the first and second light-emittingstacks 340 and 350.

For example, the N-type charge generation layer 362 may supply electronsto the first light-emitting stack (ST1) 340 adjacent to the firstelectrode 310. The P-type charge generation layer 364 may supply holesto the second light-emitting stack (ST2) 350, and the second holetransport layer 351 may supply holes to the second light-emitting stack(ST2) 350 adjacent to the second electrode 320.

The N-type charge generation layer 362 may be formed to constitute ahost-dopant system, and thus may include an N-type dopant material andan N-type host material. The N-type dopant material may include Group Iand II metals on the periodic table, organic materials capable ofsupplying electrons, or a mixture thereof. For example, the N-typedopant material may include one of an alkali metal and an alkali earthmetal. For example, the N-type charge generation layer 362 may be anorganic layer formed by doping with an alkali metal, such as lithium(Li), sodium (Na), potassium (K), and cesium (Cs); or an alkali earthmetal, such as magnesium (Mg), strontium (Sr), barium (Ba), and radium(Ra), without being limited thereto. The N-type host material mayinclude at least one material capable of supplying electrons and mayinclude one or more of, for example: tris(8-hydroxyquinolino)aluminum(Alq₃), 8-hydroxyquinolinolato-lithium (Liq),2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD),3-(4-biphenyl)4-phenyl-5-tert-butylphenyl-1,2,4-triazole (TAZ),spiro-PBD, bis(2-methyl-8-quinolinolate)-4-(phenylphenolato)aluminum(BAlq), SAlq,2,2′,2-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole (TPBi),oxadiazole, triazole, phenanthroline, benzoxazole, and benzthiazole,without being limited thereto.

Alternatively, the N-type charge generation layer 362 may not constitutethe host-dopant system. For example, the N-type charge generation layer362 may be free from the N-type dopant material. The P-type chargegeneration layer 364 may include a P-type dopant material and a P-typehost material. The P-type charge generation layer 364 may be on theN-type charge generation layer 362 to form a PN junction together withthe N-type charge generation layer 362. The P-type dopant material mayinclude a metal oxide, an organic material, such astetrafluoro-tetracyanoquinodimethane (F4-TCNQ),hexaazatriphenylenehexacarbonitrile (HAT-CN), hexaazatriphenylene, andthe like; or may include a metallic material, such as V₂O₅, MoO_(x), andWO₃, without being limited thereto. The P-type host material may includeat least one material capable of transferring holes selected from thegroup consisting of, for example, N,N-dinaphthyl-N,N′-diphenyl benzidine(N,N′-bis(naphthalene-1-yl)-N,N′-bis(phenyl)-2,2′-dimethyl benzidine,NPD), N,N′-bis-(3-methylphenyl)-N,N′-bis-(phenyl)-benzidine (TPD), and4,4′,4-tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine (MTDATA),without being limited thereto.

The additional light-emitting stack may emit red (R), green (G), oryellow (Y) light. In one embodiment, the first light-emitting stack(ST1) 340 may emit blue light and the second light-emitting stack (ST2)350 may emit green (G), yellow green (YG), yellow (Y), or orange light,which has a longer wavelength than the blue light.

In one embodiment, the organic light-emitting diode may be a whiteorganic light-emitting diode which has luminous characteristics of red(R), green (G), and blue (B) colors, which are the three primary colorsof light. For example, in the white organic light-emitting diode, thefirst light-emitting stack (ST1) 340 may emit blue light, and the secondlight-emitting stack (ST2) 350 may include one host material and ayellow dopant to emit yellow (Y) light, such that the white organiclight-emitting diode may emit blue and yellow light, thereby realizingwhite light. In operation of the white organic light-emitting diode,white light can be realized through mixture of light emitted from thefirst light-emitting stack (ST1) 340 and light emitted from the secondlight-emitting stack (ST2) 350. The organic light-emitting diode may beused, for example, in an organic light-emitting display and a lightingapparatus.

In accordance with another aspect of the present disclosure, there maybe provided an organic light-emitting display. The organiclight-emitting display may include a substrate, an organiclight-emitting diode disposed above the substrate, and a driving devicebetween the substrate and the organic light-emitting diode and connectedto the first electrode.

FIG. 5 is a sectional view of an organic light-emitting displayaccording to one example embodiment of the present disclosure.

With reference to FIG. 5, an organic light-emitting display 400according to one example embodiment may include a substrate 401, anorganic light-emitting diode 500, and an encapsulation layer 490covering the organic light-emitting diode 500. A thin film transistorTd, acting as a driving device, and the organic light-emitting diode500, connected to the thin film transistor Td, may be on the substrate401.

Although not shown in the drawings, the organic light-emitting displaymay further include a gate line and a data line intersecting each otherto define a pixel region, a power line extending parallel to one of thegate line and the data line and separated therefrom, a switching thinfilm transistor connected to the gate line and the data line, and astorage capacitor connected to the power line and one electrode of theswitching thin film transistor on the substrate 401.

The thin film transistor Td may be connected to the switching thin filmtransistor, and may include a semiconductor layer 410, a gate electrode430, a source electrode 452 and a drain electrode 454. The semiconductorlayer 410 may be on the substrate 401, and may include an oxidesemiconductor material or polycrystalline silicon. When thesemiconductor layer 410 includes the oxide semiconductor material, alight shielding pattern (not shown) may be provided under thesemiconductor layer 410 to reduce or prevent degradation of thesemiconductor layer 401 due to light by blocking light from entering thesemiconductor layer 410. Alternatively, the semiconductor layer 410 mayinclude polycrystalline silicon. In this alternative embodiment, bothedges of the semiconductor layer 410 may be doped with impurities.

A gate insulation layer 420 including an insulating material may beformed over the substrate 401 to be disposed on the semiconductor layer410. The gate insulation layer 420 may be formed of an inorganicinsulating material, such as silicon oxide or silicon nitride.

The gate electrode 430 may include a conductive material, such as ametal, and may be at a location on the gate insulation layer 420corresponding to the center of the semiconductor layer 410. The gateelectrode 430 may be connected to the switching thin film transistor.

An interlayer insulation layer 440 may include an insulating materialover the substrate 401 to be on the gate electrode 430. The interlayerinsulation layer 440 may include an inorganic insulation material, suchas silicon oxide or silicon nitride, or an organic insulation material,such as benzocyclobutene or photo-acryl.

The interlayer insulation layer 440 may include first and secondsemiconductor layer contact holes 442, 444, which may respectivelyexpose opposite sides of the semiconductor layer 410. The first andsecond semiconductor layer contact holes 442, 444 may be at oppositesides of the gate electrode 430 to be separated therefrom.

A source electrode 452 and a drain electrode 454 including a conductivematerial may be on the interlayer insulation layer 440. The sourceelectrode 452 and the drain electrode 454 may be separated from eachother around the gate electrode 430, and may respectively contact theopposite sides of the semiconductor layer 410 through the first andsecond semiconductor layer contact holes 442, 444. The source electrode452 may be connected to the power line (not shown).

The semiconductor layer 410, the gate electrode 430, the sourceelectrode 452, and the drain electrode 454 may constitute the thin filmtransistor Td. In this example embodiment, the thin film transistor Tdhas a coplanar structure wherein the gate electrode 430, the sourceelectrode 452 and the drain electrode 454 may be on the semiconductorlayer 410.

Alternatively, the thin film transistor Td may have an invertedstaggered structure in which the gate electrode may be at a lower sideof a semiconductor layer, and the source electrode and the drainelectrode may be at an upper side of the semiconductor layer. In thisstructure, the semiconductor layer may include non-crystalline silicon.On the other hand, the switching thin film transistor (not shown) mayhave a substantially similar structure as the thin film transistor Td.

The organic light-emitting display 400 may include a color filter 460that may absorb or pass light emitted from the organic light-emittingdiode 500. For example, the color filter 460 can absorb or pass red (R),green (G), blue (B), and/or white (W) light. In this case, each of thecolor filter patterns adapted to absorb or pass red, green, and bluelight may be separately formed in the corresponding pixel region tooverlap an organic light-emitting layer 530 of the organiclight-emitting diode 500, which may emit light in a wavelength band tobe absorbed or passed by the corresponding color filter pattern. Withthe color filter 460, the organic light-emitting display 400 can realizefull-color display.

For example, when the organic light-emitting display 400 is abottom-emission type, the color filter 460 for absorbing light may be onthe interlayer insulation layer 440 that corresponds to the organiclight-emitting diode 500. In an alternative embodiment, in which theorganic light-emitting display 400 is a top-emission type, the colorfilter may be on the organic light-emitting diode 500, for example, onthe second electrode 520. By way of example, the color filter 460 mayhave a thickness of about 2 μm to 5 μm. In this example embodiment, theorganic light-emitting diode 500 may be a white light-emitting diodehaving a tandem structure, as shown in FIG. 4.

A protective layer 470 may cover the thin film transistor Td. Theprotective layer 470 may include a drain contact hole 472 that mayexpose the drain electrode 454.

A first electrode 510 may be on the protective layer 470 to beseparately disposed in each pixel region, and may be connected to thedrain electrode 454 of the thin film transistor Td through the draincontact hole 472. The first electrode 510 may be an anode, and mayinclude a conductive material having a relatively high work function.For example, the first electrode 510 may be formed of a transparentconductive material, such as ITO, IZO, or ZnO.

On the other hand, when the organic light-emitting display 400 is atop-emission type, a reflective electrode or a reflective layer may befurther provided on a lower surface of the first electrode 510. Forexample, the reflective electrode or the reflective layer may includeone or more of: aluminum (Al), silver (Ag), nickel (Ni), and/or analuminum-palladium-copper (APC) alloy. Embodiments are not limited tothese examples.

A bank layer 486 may be provided on the protective layer 470 to cover anedge of the first electrode 510. The bank layer 480 may expose a centralregion of the first electrode 510 corresponding to the pixel region.

A light-emitting stack 530 may be on the first electrode 510. By way ofexample, the light-emitting stack 530 may include at least twolight-emitting stacks, as shown in FIG. 4, to form a tandem structure ofthe organic light-emitting diode 500.

A second electrode 520 may be on the light-emitting stack 530, and maybe above the substrate 401. The second electrode 520 may be over adisplay region, and may include a conductive material having arelatively low work function to be used as a cathode. For example, thesecond electrode 520 may include one or more of: aluminum (Al),magnesium (Mg), and/or an AlMg alloy. Embodiments are not limited tothese examples.

The first electrode 510, the light-emitting stack 530, and the secondelectrode 520 may constitute the organic light-emitting diode 500. Anencapsulation layer 490 may be provided on the second electrode 520 toreduce or prevent external moisture from entering the organiclight-emitting diode 500. Although not shown in the drawings, theencapsulation layer 490 may have a trilayer structure in which a firstinorganic layer, an organic layer, and a second inorganic layer may besequentially stacked, without being limited thereto.

Next, an example embodiment of the present disclosure will be describedin more detail with reference to examples. However, it should be notedthat these examples are provided for illustration only and should not beconstrued in any way as limiting the disclosure.

EXPERIMENTAL RESULTS Example 1

In a vacuum chamber at a pressure of 5×10⁻⁸ to 7×10⁻⁸ torr, an organiclight-emitting diode was fabricated by sequentially depositing a holeinjection layer, a hole transport layer (HTL1), a blue light-emittinglayer (blue host material (BH) and blue fluorescent dopant material (BD,4 wt % doping)), an electron transport layer (ETL1), an electroninjection layer (LiF) and a cathode on an ITO substrate (anode).

FIG. 6 is an energy diagram depicting energy levels of an organiclight-emitting diode of Example 1.

FIG. 6 is an energy diagram depicting the energy levels ofHTL1/BH+BD/ETL1 of the fabricated organic light-emitting diode. Inevaluation of the energy level, it could be seen that, in the fabricatedorganic light-emitting diode, the difference between the HOMO energylevel of HTL1 and the HOMO energy level of BD was 0.1 eV or less and thedifference between the LUMO energy level of ETL1 and the LUMO energylevel of BD was 0.1 eV or less. With reference to FIG. 6, the differencebetween the HOMO energy level of HTL1 and the HOMO energy level of BD is0.1 eV or less and the difference between the LUMO energy level of ETL1and the LUMO energy level of BD is 0.1 eV or less, as indicated bydotted lines.

Comparative Example 1

In a vacuum chamber at a pressure of 5×10⁻⁸ to 7×10⁻⁸ torr, an organiclight-emitting diode was fabricated by sequentially depositing a holeinjection layer, a hole transport layer (HTL2), a blue light-emittinglayer (blue host material (BH) and blue fluorescent dopant material (BD,4 wt % doping)), an electron transport layer (ETL2), an electroninjection layer (LiF) and a cathode on an ITO substrate (anode).

FIG. 7 is an energy diagram depicting energy levels of an organiclight-emitting diode of Comparative Example 1.

FIG. 7 is an energy diagram depicting the energy levels ofHTL2/BH+BD/ETL2 of the fabricated organic light-emitting diode ofComparative Example 1. In evaluation of the energy level, it could beseen that, in the fabricated organic light-emitting diode, thedifference between the HOMO energy level of HTL2 and the HOMO energylevel of BD was greater than 0.1 eV and the difference between the LUMOenergy level of ETL2 and the LUMO energy level of BD was greater than0.1 eV. With reference to FIG. 7, the difference between the HOMO energylevel of HTL2 and the HOMO energy level of BD is greater than 0.1 eV andthe difference between the LUMO energy level of ETL2 and the LUMO energylevel of BD is greater than 0.1 eV, as indicated by dotted lines.

Materials used in Example 1 and Comparative Example 1 and energy levelsthereof are shown as follows:

HOMO LUMO T₁ Name Structure (eV) (eV) (eV) HTL1

−5.79 −2.57 2.82 HTL2

−5.50 −2.42 2.52 ETL1

−6.21 −2.73 2.67 ETL2

−5.99 −2.98 2.1  BH

−6.00 −2.99 1.85 BD

−5.61 −2.81 —

Experimental Example 1: Evaluation of Characteristics of OrganicLight-Emitting Diode (Above)

Operation characteristics of the organic light-emitting diodesfabricated in Example 1 and Comparative Example 1 were evaluated. Table1 shows voltage-current density, brightness-current efficiency,brightness-external quantum efficiency (EQE), and lifespan of theorganic light-emitting diodes fabricated in Example 1 and ComparativeExample 1.

TABLE 1 Voltage-current Brightness-external Voltage density quantumefficiency Lifespan Item (V) (Cd/A) (EQE) (hours) Example 1 3.7 8.0 8.150 Comparative 4.5 6.0 6.2 30 Example 1

The organic light-emitting diode of Comparative Example 1 had a largerdifference in HOMO energy level between HTL2 and BH than that of Example1 and ETL2 had a lower LUMO energy level than BD in ComparativeExample 1. As a result, Comparative Example 1 did not satisfy thefollowing conditions:

(F) The hole transport layer material has a higher HOMO energy levelthan the blue fluorescent dopant material and a difference in HOMOenergy level between the hole transport layer material and the bluefluorescent dopant material is 0.1 eV or less (the difference betweenthe HOMO energy levels was greater than 0.1 eV in Comparative Example1); and

(G) the electron transport layer material has a higher LUMO energy levelthan the blue fluorescent dopant material and a difference in LUMOenergy level between the electron transport layer material and the bluefluorescent dopant material is 0.1 eV or less (the difference betweenthe LUMO energy levels was greater than 1.0 eV in Comparative Example1).

From Table 1, it could be seen that the organic light-emitting diodeprepared in Comparative Example 1 had poorer operation characteristicsand shorter lifespan than the organic light-emitting diode prepared inExample 1.

It will be apparent to those skilled in the art that variousmodifications and variations may be made in the present disclosurewithout departing from the technical idea or scope of the disclosure.Thus, it is intended that embodiments of the present disclosure coverthe modifications and variations of the disclosure provided they comewithin the scope of the appended claims and their equivalents.

LIST OF REFERENCE NUMERALS

-   -   100, 200, 300, 500: organic light-emitting diode    -   110, 210, 310, 410, 510: first electrode    -   120, 220, 320, 420, 520: second electrode    -   140, 240, 530: light-emitting stack    -   141, 241, 341, 351: hole transport layer    -   142, 242, 342, 352: blue light-emitting layer    -   144, 244, 344, 354: hole transport layer    -   243: hole injection layer    -   244: electron transport layer    -   245: electron injection layer    -   340: first light-emitting stack    -   350: second light-emitting stack    -   360: charge generation layer    -   362: N-type charge generation layer    -   364: P-type charge generation layer    -   400: organic light-emitting display

What is claimed is:
 1. An organic light-emitting diode, comprising: afirst electrode; a light-emitting stack on the first electrodecomprising, sequentially stacked on the first electrode: a holetransport layer comprising a hole transport layer material; a bluelight-emitting layer comprising: a blue host material; and a bluefluorescent dopant material; and an electron transport layer comprisingan electron transport layer material; and a second electrode on thelight-emitting stack, wherein the hole transport layer is in contactwith the blue light-emitting layer, wherein the blue fluorescent dopantmaterial comprises a pyrene amine derivative material, wherein the bluehost material comprises an anthracene-based material, wherein theelectron transport layer material comprises a pyrimidine-based material,wherein the hole transport layer material comprises a tertiaryamine-based material, wherein the blue fluorescent dopant material has ahigher LUMO (Lowest Unoccupied Molecular Orbital) energy level than theblue host material, wherein the blue fluorescent dopant material has ahigher HOMO (Highest Occupied Molecular Orbital) energy level than theblue host material, wherein the blue fluorescent dopant material has alower singlet energy than the blue host material, wherein the holetransport layer material has a higher HOMO energy level than the bluehost material, wherein the electron transport layer material has ahigher LUMO energy level than the blue host material, wherein theelectron transport layer material has a higher LUMO energy level thanthe blue fluorescent dopant material, wherein a difference in LUMOenergy level between the electron transport layer material and the bluefluorescent dopant material is 0.1 eV or less, wherein thelight-emitting stack is a first light-emitting stack, wherein at leastone additional light-emitting stack, comprising a second light-emittingstack, is further between the first electrode and the second electrode,wherein the organic light-emitting diode further comprises a chargegeneration layer between the first light-emitting stack and the secondlight-emitting stack, wherein the charge generation layer comprises anN-type charge generation layer and a P-type charge generation layer,wherein the N-type charge generation layer excludes an anthracene-basedmaterial, and wherein the N-type charge generation layer comprises anorganic material.
 2. The organic light-emitting diode of claim 1,wherein the blue light-emitting layer comprises 1 wt % to 5 wt % of theblue fluorescent dopant material.
 3. The organic light-emitting diode ofclaim 1, wherein the organic light-emitting diode comprises a whiteorganic light-emitting diode comprising the at least one additionallight-emitting stack configured to emit red (R), green (G), or yellow(Y) light.
 4. A method of manufacturing an organic light-emitting diode,the method comprising: providing a first electrode; providing alight-emitting stack on the first electrode comprising, sequentiallystacking on the first electrode: a hole transport layer comprising ahole transport layer material; a blue light-emitting layer comprising: ablue host material; and a blue fluorescent dopant material; and anelectron transport layer comprising an electron transport layermaterial; and providing a second electrode on the light-emitting stack,wherein the hole transport layer is in contact with the bluelight-emitting layer, wherein the providing the blue fluorescent dopantmaterial comprises providing a pyrene amine derivative material, whereinthe providing the blue host material comprises providing ananthracene-based material, wherein the providing the electron transportlayer material comprises providing a pyrimidine-based material, whereinthe hole transport layer material comprises a tertiary amine-basedmaterial, wherein the blue fluorescent dopant material has a higher LUMO(Lowest Unoccupied Molecular Orbital) energy level than the blue hostmaterial, wherein the blue fluorescent dopant material has a higher HOMO(Highest Occupied Molecular Orbital) energy level than the blue hostmaterial, wherein the blue fluorescent dopant material has a lowersinglet energy than the blue host material, wherein the hole transportlayer material has a higher HOMO energy level than the blue hostmaterial, wherein the electron transport layer material has a higherLUMO energy level than the blue host material, wherein the electrontransport layer material has a higher LUMO energy level than the bluefluorescent dopant material, wherein a difference in LUMO energy levelbetween the electron transport layer material and the blue fluorescentdopant material is 0.1 eV or less, wherein the light-emitting stack is afirst light-emitting stack, wherein at least one additionallight-emitting stack, comprising a second light-emitting stack, isfurther between the first electrode and the second electrode, whereinthe organic light-emitting diode further comprises a charge generationlayer between the first light-emitting stack and the secondlight-emitting stack, wherein the charge generation layer comprises anN-type charge generation layer and a P-type charge generation layer,wherein the N-type charge generation layer excludes an anthracene-basedmaterial, and wherein the N-type charge generation layer comprises anorganic material.
 5. The method of claim 4, wherein the bluelight-emitting layer comprises 1 wt % to 5 wt % of the blue fluorescentdopant material.
 6. The method of claim 4, wherein the providing theorganic light-emitting diode comprises providing a white organiclight-emitting diode comprising the at least one additionallight-emitting stack configured to emit red (R), green (G), or yellow(Y) light.